Fuel Cells

Question 1

Primary cells

Answer 1

contain a fixed amount of reactant
discarded once discharged
cheap + easily manufactured
voltage drops from start of use

Question 2

Secondary cells

Answer 2

rechargeable
recharged by applying a DC voltage in reverse direction to the discharge current

Question 3

Fuel cells

Answer 3

Different to primary + secondary as they do not store reactants but they are continuously fed into fuel cell
long life
use a type of fuel (hydrogen)

Question 4

Example + equation- primary

Answer 4

Leclanche

Zn(s) + 2MnO2(s) + 2NH4+(aq)  Zn2+(aq) + Mn2O3(s) + 2NH3(g) +H2O(ℓ)

Question 5

Example + equation- secondary

Answer 5

lead acid accumulator

Pb(s) + PbO2(s) + 4 H+(aq) + 2 SO42-(aq)  2 PbSO4(s) + 2 H2O(ℓ)

Question 6

Example + equation- fuel cell

Answer 6

alkaline hydrogen fuel cell

2 H2(g) + O2(g)  2 H2O(ℓ)

Question 7

Fuel cell electric vehicle

Answer 7

run using a fuel source that is stored in the vehicle + pumped to the cell where electricity is produced
hydrogen is the most common
electricity produced is used to power an electric motor

Question 8

Tesla

Answer 8

stores electricity
uses some variation of the lithium ion cell

Question 9

advantages of hydrogen fuel cells over internal combustion engine to power transport

Answer 9

more energy efficient as they involve controlled oxidation of the fuel + not combustion

only produces water as a product, compared to gasoline/diesel which produces CO2, as well as sulfur dioxide, nitrogen oxides and particulates

Question 10

disadvantages of hydrogen fuel cells over internal combustion engine to power transport

Answer 10

fossil fuels are used to produce hydrogen which contributes to greenhouse gas emissions

hydrogen is very flammable and releases a lot of heat per kg so is considered more dangerous

Question 11

How is hydrogen produced?

Answer 11

steam-methane reforming reaction
CH4 (natural gas) + H2O  CO + H2

subsequently followed by the water-gas shift reaction
CO + H2O  CO2 + H2 + heat

electrolysis

Question 12

Can H2 production by considered low-emission?

Answer 12

Steam-methane reforming process requires fossil fuels which are non-renewable + contributes to increase of CO2 in atmosphere

electrolysis of water- renewable energy source needed in order to be considered ‘clean’ energy source

greenhouse effect
rising sea levels

Question 13

Importance for organisations like IPHE to exist

Answer 13

common goal– produce fuel cell to reduce carbon footprint
make new technologies accessible

Question 14

Recent initiative influenced by IPHE

Answer 14

hydrogen Guarantee of Origin scheme
measure and track emissions from hydrogen production + type of technology used to manufacture the hydrogen

Question 15

Fuel cell components

Answer 15

Anode- porous nickel

Cathode- porous nickel oxide

Electrolyte- potassium hydroxide (KOH) solution - alkaline

Question 16

Fuel cell EMF

Answer 16

0.4 + 0.83 = 1.23V

Question 17

Anode discharge reaction

Answer 17

2H2(g) + 4OH-(aq)  4H2O(l) + 4e-

Question 18

Cathode discharge reaction

Answer 18

O2(g) + 2H2O(l) + 4e-  4OH-(aq)

Question 19

Overall discharge redox reaction

Answer 19

2H2(g) + O2(g)  2H2O(l)